NEW YORK (Reuters Health) - Programs designed to prevent childhood obesity in the home don't affect kids' weight a year or more down the line, according to a review of the evidence.

But that conclusion comes from only a small number of available studies on the programs, and doesn't prove that such studies can't work, according to lead author Dr. Nakiya Showell.

"We need additional studies to answer this question, especially studies with greater number of participants, greater program exposure among participants and longer participant followup," said Showell, of Johns Hopkins University School of Medicine in Baltimore.

Other studies have shown that family influence and home environment play an important role in preventing childhood obesity, which affects about 17 percent of American children, according to the Centers for Disease Control and Prevention.

For the review, the researchers analyzed the results of the six best studies on home based programs for kids. Three included diet and exercise, one was on diet alone and two also included primary care or school programs. The kids ranged from two to 18 years old.

The studies either compared the home-based program to another program or to a comparison group of kids not enrolled in any program. All measured the kids' weight or body mass index (BMI), an indication of body fat percentage, at least one year after the program had ended, to see if it had any effect.

Some of the programs did result in kids eating more fruits and veggies or getting up and moving around more than the comparison groups, but none affected kids' weight or BMI, according to results published in the journal Pediatrics.

In each study, the percentage of kids qualifying as overweight or obese was the same in the program group and the comparison group.

Among the three studies that showed the programs worked, although not for weight, the findings may have been because those programs had components in schools or primary care.

There isn't enough evidence out there to draw real conclusions about these programs, according to Helen Skouteris, who was not involved in the study.

And the few that were available for study included children in a wide range of ages, in fact too wide a range to synthesize the results, Skouteris, of Deakin University in Burwood Victoria, Australia, told Reuters Health.

It is also troubling that the study did not include details about parental influences like role modeling, encouragement and feeding behaviors, which should not be ignored, she said.

It's unclear how best to improve these programs, but "In my opinion as a pediatrician and pediatric obesity researcher, home-based obesity prevention programs should include additional components beyond what is described in this particular review," Showell said.

The programs should stress family and parental involvement and also address access to healthy food and space for play in the community, she said.